Trilobite Systematics

Trilobites US

Trilobite Systematics and Taxonomic Relationships

Phylogenetics is the study of evolutionary relationships (progenitors, descendents, and evolutionary branching) among groups of organisms. The relationships are hypothesized through morphological data for fossils, and with molecular phylogenetics using nucleotide sequences encoding genes or amino acid sequences encoding proteins for extant organisms. Obviously, sequencing of trilobite genes and proteins is impossible, and so trilobite phylogenetics is largely based on cladistics,an approach to biological classification where organisms are grouped together based on whether or not they share morphological traits (particularly unique characteristics) derived from the group's last common ancestor, and that are not present in more distant ancestors. The process results in an evolutionary taxonomy that shows ancestral progenitors and descendants in a tree-like structure.

Taxonomy and Phylogeny within Class Trilobita

The taxonomy and basic phylogeny of Class Trilobita are shown below that are mostly consistent with the 1997 Treatise on Invertebrate Paleontology, Part O (Trilobita) and Richard Fortey's important 2001 work summarizing 75 years of trilobite systematics, where Fortey laments that despite "complex morphology and a long geological
history with an apparently good fossil record, their systematics is still in an unsatisfactory state".

Trilobite Taxonomy
Trilobite Phylogeny
Phylum Arthropoda
Subphylum Chelicerata
or Subphylum Trilobitamorph
Superclass Arachnomorpha (1)
Class Trilobita

    Order Agnostida
    Order Redlichiida
    Order Corynexochida
    Order Phacopida
    Order Lichida
    Order Odontopleurida (2)
    Order Proetida
    Order Harpetida
    Order Ptychopariida
    Order Asaphida
    Order Nectaspida
o Arthropoda
`--o Trilobita
   `--+--o Redlichiida
      |  |--Olenellina
      |  `--Redlichiina
      `--o Librostoma
(1) Several alternative taxonomies are found in past and current literature. For example, trilobites are sometimes found placed in Arthropoda Subphylum Schizoramia within Superclass Arachnomorpha.
(2) Some authors argue that a new Order Odontopleurida should be separated (erected) from Order Lichida, and it appears such a revision will be eventually sustained.

Trilobite systematics chart, sensu Fortey (2001) - click hotspots to link to classification pages for individual trilobite orders or suborders:

Trilobite systematics chart sensu Fortey


Agnostida Classification Agnostida Suborder Eodiscina Classification Agnostida Suborder Agnostina Classification Asaphida Trilobites Classification Ptychopariida Suborder Olenina Trilobites Classification Ptychopariida Suborder Olenina Trilobites Classification Ptychopariida Trilobites Classification Redlichiida Trilobites Classification Redlichiida Suborder Olenellina Trilobites Classication Redlichiida Suborder Redlichiina Trilobites Classification Proetida Trilobites Classification Harpetida Trilobites Classification Lichida Trilobites Classification Odontopleurida Trilobites Classification Corynexochida Trilobites Classification Order Phacopida Trilobites Classification Phacopina